This paper describes a system for compressed code generation. The code of applications is partioned into time-critical and non-time-critical code. Critical code is compiled to native code, and non-critical code is compiled to a very dense virtual instruction set which is executed on a highly optimized interpreter. The system employs dictionary-based compression by means of superinstructions which correspond to patterns of frequently used base instructions. The code compression system is designed for the Philips TriMedia VLIW processor. The interpreter is pipelined to achieve a high interpretation speed. The pipeline consists of three stages: fetch, decode, and execute. While one instruction is being executed, the next instruction is decoded, and the next one after that is fetched from memory. On a TriMedia VLIW with a load latency of three cycles and a jump latency of four cycles, the interpreter achieves a peak performance of four cycles per instruction and a sustained performance of 6.27 cycles per instruction. Experiments are described that demonstrate the compression quality of the system and the execution speed of the pipelined interpreter; these were found to be about five times more compact than native TriMedia code and a slowdown of about eight times, respectively.
No abstract
Abstract. The performance of a Java Virtual Machine (JVM) interpreter running on a very long instruction word (VLIW) processor can be improved by means of pipelining. While one bytecode is in its execute stage, the next bytecode is in its decode stage, and the next bytecode is in its fetch stage. The paper describes how we implemented threading and pipelining by rewriting the source code of the interpreter and several modifications in the compiler. Experiments for evaluating the effectiveness of pipelining are described. Pipelining improves the execution speed of a threaded interpreter by 19.4% in terms of instruction count and 14.4% in terms of cycle count. Most of the simple bytecodes, like additions and multiplications, execute in four cycles. This number corresponds to the branch latency of our target VLIW processor. Thus most of the code of the interpreter is executed in branch delay slots.
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